The purpose of the present proposal is to study the properties of the gas exchange system at the levels of the lung, blood and tissue. The following studies are proposed: 1) To assess the role of specific environmental stresses on VA/Q distribution under situations of pulmonary gas embolization, high ambient pressure or water immersion; 2) To identify and quantify the anomolous behavior of CO2 in normal breathing humans; 3) To study the influence of cyanate, pH, base excess, carbon monoxide and 2,3-diphosphogylcerate on the hemoglobin oxygen dissociation curve; 4) To separate the pH-mediated versus oxygen saturation-mediated influences of hypoxia on 2,3-DPG production in the red cell; and 5) To quantitate the influence of altered hemoglobin-oxygen affinity on oxygen delivery.